The invention is a vehicle wheel, particularly adapted for use for a passenger car though the vehicle wheel can be utilized in conjunction with most any vehicle, such as truck or automobile wheels, motorcycle wheels, bicycle wheels or similar two-wheel vehicles.
In order to increase the driving comfort of vehicles, the motor vehicle industry is increasingly confronted with deadening structure-borne noise arising from the rolling of tires that adversely affects the passenger compartment through wheels, axles, axle suspension and chassis.
It is known from WO-A-99/55542, DE-A-198 19 128, DE-A-44 00 912 and EP-A-0029 120 to place sound absorbing material on the exterior wheel rim and/or the inner tire. In the case of sound absorbing fibers, they are arranged in a ball, intertwined and placed in a perforated wrapping ringed around the wheel rim and jutting out into the interior wheel (see e.g. FIGS. 5 and 6 from EP-A-0 029 120). From DE-A-38 23 157 a surface formation coated with flock fibers is known that can be used for noise deadening purposes.
Even though conventional vehicle wheels posses good noise deadening properties due to the use of noise deadening materials, these systems have the disadvantage that the mounting of noise absorption material and tire to the wheel rim requires considerable work.
The invention is a vehicle wheel with a sound absorbing material that is easy to fit and to remove without damaging the sound absorbing material, and thus noise absorbing properties during wheel operation are reduced.
In order to reduce vehicle wheel sounds the invention proposes a vehicle wheel, especially for motor vehicles such as passenger cars, equipped with a wheel disk adapted to be mounted for rotation about a rotation axis, a wheel rim linked to the wheel disk and having an exterior side curved or turned away from the disk, an airborne sound absorbing fiber material arranged on the outside surface of the wheel rim, the fiber material has a carrier layer resting on the outside surface of the rim with an underside of the carrier layer contacting the outside surface of the rim and its outer surface having fibers jutting out away from the outside rim, and the carrier layer is held to the outside surface of the rim.
Every vehicle wheel has a wheel rim serving as a receptacle and holding device for the wheel. The wheel rim itself is linked to the rotation axis through the so-called wheel disk. The wheel disk and rim generally consist of metal (steel or light metal). According to the invention, an airborne sound absorbing fiber material is attached to the outside surface of the rim which, with the wheel mounted thereon, is interiorly of the wheel. This material is mechanically stable, temperature resistant, and is reliably fixed to the rim to resist mechanical strains (centrifugal forces during wheel operation and transverse loads during mounting and dismounting tires) and temperature impacts (in the interior tire and at the rim, temperatures of up to 120xc2x0 C. can arise).
The fiber material has a carrier layer, preferably arranged around the rim in the form of a strip and attached to the rim. Fibers jut out from the carrier layer, are loop-shaped, or the fiber ends project away from the carrier layer. Fiber material, such as loops, plush, single fibers, yarns (crossing fibers) or felt whose fibers are embedded in the carrier layer are suitable as sound absorbing fiber material.
In order to keep the xe2x80x9crotating massxe2x80x9d produced by the vehicle wheel in spite of the airborne sound absorbing material as low as possible, it is advantageous for the sound absorbing material to be light weight, such as synthetic fiber material (polyamide, polyacryle, polyester, PP, viscose) having fibers anchored to the light-weight carrier layer. The carrier layer should be mechanically stable and resistive to high tensile stress at times caused by extreme centrifugal forces occurring from the rotation of the vehicle wheel and transverse loads experienced during mounting and dismounting of tires.
Plush materials made from synthetic fibers, natural fibers or a blend of both are conventionally available as sound absorbing material. These plush materials are used for various purposes. Plush material can, for instance, be found on the backside of seat covers made from lamb""s wool and as fill for rag animals. Tests have shown that excellent sound absorbing properties can be obtained with plush material having a fiber length between 10 mm and 25 mm (fiber length is equal to the distance between free end of fiber and the carrier layer). The weight per unit area of the plush material is between approximately 300 and 1800 g/m2. Fiber materials with a weight per unit area (fibers and carrier layer) of up to 3 kg /m2, preferably 2 kg/m2 and especially up to 1.5 kg/m2, can be used as sound absorbing material.
The greater the density and length of the fibers of the fiber material used as airborne sound absorbing material the better will be the sound absorbing effect of the fiber material. The length of fibers can, however, be limited. The mounting of the tire cannot be constrained in spite of the sound absorbing material attached to the rim.
Tests have shown that fiber length of 5 mm to 40 mm, especially 10 to 25 mm and preferably 12 to 20 mm, allow a good compromise between easy mounting of the tire and sound absorbing properties of the fiber material. The sound absorbing material can, under consideration of the above mentioned conditions, only be attached to the area of the rim in which the outside surface is below the level of (has a lesser circumference than) the bearing areas of the tire beads. Most of the time, this is possible in the central axial area of the rim between the rim beads. However, the sound absorbing material should not be placed into the so-called drop base rim or well base rim (depression of rim in an outside surface).
The distance between absorbing fiber material and inner bearing areas of the rim, i.e. areas farther from the wheel disk, should be at least equal to the maximum height of the sound absorbing material layer. In the case of a fiber material with fibers jutting out from a carrier layer and having a certain length, the distance described above should be at least equal to the fiber length. This is due to the fact that in such a case fibers which lay down because of the push of the inner tire bead over the fiber material during tire mounting do not enter the bearing area. The bearing area should be free of impurities that can also consist of fibers, since tight bead-to-bead contact of the tire to the rim is a prerequisite in this area.
The carrier layer is either a woven textile to which the fibers are anchored or a layer of, e.g. adhesive, in which the fibers are partly embedded. In case of a woven carrier layer, the fibers are woven into the carrier layer and are thereby anchored to the carrier layer at their middles. In the case of a monolithic carrier layer, the fibers are embedded into the carrier layer through a special technology, i.e. a flocking process. The embedded ends of the fibers can be enlarged so as to be anchored more reliably into the carrier layer.
The invention counteracts vibrations that, caused by excitation of surfaces, generally create vehicle wheel contortion. Vibrations arising when vehicle wheels cross very rough surfaces or cross joints/edges/cross grooves are also avoided or reduced. The deformations of the tire in the area of the running surface lying on the ground lead to a transient vibration of the gas volume enclosed in the tire. The basic natural oscillation results from the length of the unrolled channel formed by rim and tire. The basic natural oscillation is usually between 200 Hz and 350 Hz and is mainly determined by the length of the channel (medium circumference of tire). Since the tire is relatively soft and all peripheries within the volume have even surfaces, with some determined frequencies a hum develops similar to echoes in rooms. As a consequence of the hum, tire and rim as components bordering the channel are themselves excited to vibrations (structure-borne noise) of the same or similar frequencies, which are then, as structure-borne noise, imparted to the vehicle""s bodywork through wheel hub, steering knuckles, and axle shaft. A part of the noise, however, penetrates the passenger compartment as direct airborne noise and is additionally perceptible to passers-by as disturbing traffic noise.
Through the addition of airborne sound absorbing fiber material to vehicle wheels, several advantages effects are produced. The distinct natural oscillations are shifted towards lower frequencies by some Hertz (usually 5 Hz to 30 Hz). The sound intensity level of the individual natural oscillation spikes is reduced. The shift towards lower frequencies and reduction of sound level increase with increasing frequency. As a result of this modification, the basic natural oscillations to be expected from the geometry of the volume and the hum can no longer arise at certain frequencies. The reverberation of the natural oscillations fades away much faster. As a consequence, tire and rim are no longer excited to natural oscillations with these disturbing frequencies, and thus, there is no transfer of sound to the neighboring structures (tire and rim). A disturbing component in the interior noisexe2x80x94excited by such a resonance of the tirexe2x80x94is no longer perceptible. The exterior noise perceptible to passers-by, when a vehicle utilizing the invention is driven over uneven ground, is also considerably reduced.
The sound absorption effected according to the invention, i.e. adding airborne noise absorbing fiber material to the rim, consists of deadening and/or avoiding the markedness of stationary waves in the interior tire, so that only a reduced transfer of noise to the neighboring structures of the vehicle wheel is possible. The reduction of the structure-borne noise affecting the vehicle body and reduced through the deformation of the vehicle tire is obtained by deadening/avoiding the xe2x80x9cintermediate stagexe2x80x9d of the markedness of stationary waves in the interior tire through the airborne noise absorbing material. Mechanisms, especially glancing absorption, do play a decisive role in this context. Glancing absorption can be obtained in an effective way with the help of sound absorbing fiber material with long fibers and high density fibers. The individual fibers of the sound absorbing fiber material are aligned radially in an orderly direction by rotation of the vehicle wheel.